1. Field of the Invention
The present invention disclosed in the specification relates to a semiconductor thin film which is formed on a substrate having an insulating surface and a semiconductor device having the semiconductor thin film as an activation layer. Particularly, the present invention relates to a constitution in the case where a crystal silicon film (crystalline silicon film) is used as a semiconductor thin film.
Incidentally, “semiconductor device” in the specification designates all of devices which function by utilizing a semiconductor and the followings are included in the category of a semiconductor device.
(1) Single element of TFT (Thin Film Transistor), IGFET (Insulated Gate Field Effect Transistor) or the like:
(2) Semiconductor circuit using the single element of (1):
(3) Electrooptical device constituted by (1), (2):
(4) Electronic device having (2), (3).
2. Description of Related Art
In recent years, a technology of constituting a thin film transistor (TFT) by using a semiconductor thin film (thickness; about several hundreds through several thousands Å) formed on a substrate having an insulating surface has attracted attention. A thin film transistor is widely applied to electronic devices such as IC (Integrated Circuit) or an electrooptical device and particularly, development thereof has been accelerated as a switching element of an image display device.
For example, trials have been carried out in respect of applying TFT to all the electric circuits of a pixel matrix circuit for individually controlling pixel regions arranged in a matrix in a liquid crystal display device, a drive circuit for controlling the pixel matrix circuit, a logic circuit (processor circuit or memory circuit or the like) for processing data signal from outside and the like.
In the current state, TFT using an amorphous silicon film as an activation layer has been reduced into practice. However, in an electric circuit where high speed operational function is requested such as a drive circuit, a logic circuit or the like, TFT using a crystal silicon film (polysilicon film, polycrystal silicon film or the like) is needed.
For example, as a method of forming a crystalline silicon film on a glass substrate, a technology disclosed in Japanese Unexamined Patent Publication No. JP-A-7-130652 and a technology disclosed in Japanese Unexamined Patent Publication No. JP-A-8-78329 by the applicant have publicly been known. According to the technologies disclosed in these publications, a crystal silicon film having excellent crystalline performance can be formed by a heating treatment at 500 through 600° C. for about 4 hrs by utilizing a catalyst element helping crystalize an amorphous silicon film.
Particularly, according to the technology disclosed in Japanese Unexamined Patent Publication No. JP-A-8-78329, crystal growth substantially parallel with a substrate face is carried out by applying the above-described technology and the inventors refer the formed crystallized region particularly as a horizontal growth region (or lateral growth region).
However, even when a drive circuit is constituted by using such a TFT, the required function cannot completely be satisfied yet. It is the current state that a high speed logic circuit requiring an extremely high speed operation of mega bit through giga bit level cannot be constituted by conventional TFT.